An alkanesulfonic acid having the general formula EQU R--(CH.sub.2).times.CH.sub.2 --SO.sub.3 H
wherein R is a hydrogen atom or the group --OH and x is an integer of 0.ltoreq..times..ltoreq.8 is publicly known and has been applied for various uses. In particular, a hydroxyalkanesulfonic acid which is encompassed within the above general formula, inter alia, 2-hydroxyethanesulfonic acid also referred to as isethionic acid has a wide variety of its utilities. For example, its ester with acrylic acid or methacrylic acid has been used as a reactive emulsifying agent, while its homopolymers or copolymers with vinyl monomers have been employed as a flocculating agent, a dispersing agent, a thickening agent and a flame retardant and the like. Also, its ester with a long chain alkylcarboxylic acid can have an excellent activity as a surfactant and has been widely employed in the field of detergents or cosmetics. Moreover, it has recently been expected typically as bonding agents for basic dyestuffs, adhesives, additives for tin- or tin solder-plating electrolytic bath and its usage has been widely spread.
There have been hitherto proposed a variety of processes for the preparation of an alkanesulfonic acid typically 2 -hydroxycthanesulfonic acid(isethionic acid).
There has been proposed, for example, by Baumstark, et al. in Chern. Ber.,1867, p. 586 a process wherein ethylene is treated with a sulfonating agent such as chlorosulfonic acid or the like or a process wherein ethylene oxide is treated with gaseous sulfurous acid.
However, it is found that the alkanesulfonic acids produced by these processes are contaminated with unfavorable impurities such as organic chlorinated products, sulfuric acid, organic sulfates or the like and are the products not suited for various application fields such as surfactants, additives for polymers and the like.
In view of this, many studies have been made for the production of an alkanesulfonic acid having a less content of impurities.
For example, Koening et al. in U.S. Pat. No. 2,892,852 have proposed a process wherein an organic thioether or a thioacetic acid ester is reacted with peracetic acid in an acetic acid solution to produce the corresponding sulfonic acid, while there has been proposed a process wherein ozone or a permanganate salt is used as an oxidizing agent in Journal Praktiche Chemie, (4), (2), Vol. 27, (1955), pp. 241-242. However, such processes have the problems of oxidizing agents being expensive or an obtainable yield being low so that they have not substantially been utilized in an industrial scale.
And, U.S. Pat. No. 4,499,028 to Longley et al. or Japanese Patent Kokai Application No. 32049/1990 by Itoh et al. disclosed a process wherein an alkali salt of isethionic acid with a high yield, which is obtained by reacting ethylene oxide with an alkali salt of bisulfuric acid according to a well-known procedure, is contacted with anhydrous hydrogen chloride in a water-miscible solvent such as an alcohol or the like. However, this process has the drawbacks that a corrosive gas is to be used and also a troublesome procedure for removing by-products of inorganic salts is to be adopted so that it is not advantageous for industrial application.
Further, U.S. Pat. No. 2,727,920 disclosed a process wherein methylmercaptan is subjected to electrolytic oxidation or oxidation with nitric acid. However, a low yield is provided in the former case, while acceleratedly raising reaction temperature should be controlled in the latter case and both are unsuited for industrial application.
On the other hand, hydrogen peroxide has favorable conditions such as inexpensive availability, safe handling and by-production of only water after completion of the reaction and the like as compared with other oxidizing agents, and then there have been made various studies to utilize it for the sulfonation reaction of mercaptan, besides the aforementioned processes.
For example, Showell et al. proposed in Journal of Organic Chemistry, Vol. 27, (1962), pp. 2853-2858 a process for the production of sulfonic acid by the oxidation of mercaptan using hydrogen peroxide in a system containing a sufficient amount of an organic acid to produce an organic peracid. However, the product obtained according to this process is contaminated with the residual carboxylic acid and percarboxylic acid
Moreover, an alkanesulfonic acid, particularly isethionic acid is difficult to be purified by means of those separation techniques widely used for removal of such impurities such as a solvent extraction method, a distillation method or the like owing to its intrinsic properties of solubility in various solvents, boiling point, polarity and the like. Then, it is highly disadvantageous in an industrial scale to carry out the oxidation with a peracid in situ as described above.
Deschrijver et al. proposed a process for the production of an alkanesulfonic acid by oxidation of an alkylmercaptan with hydrogen peroxide using as a catalyst a molybdenum or tungsten derivative. However, this process presented the problem of the product being colored and further resulted in prevention of the product from utilization in other application field, owing to the coexisting catalyst.
McGee et al. proposed in U.S. Pat. Nos. 4,910,330 and 4,987,250 a process for the production of an alkanesulfonic acid by oxidation of an alkylmercaptan with hydrogen peroxide without the aforementioned problems such as contamination of an organic acid or a catalyst.
The process by McGee et al. is excellent in that an alkanesulfonic acid can be produced without any contamination of the product by undesirable additives, but there may be required troublesome steps wherein conc. hydrogen peroxide is diluted with water (for example, up to about 30% by weight)and subsequently the dilution water (and the water by-produced during the reaction) is distilled off to conduct a temperature control in order to remove violent reaction heats. Further, in contacting raw materials with an oxidizing agent, an alkylmercaptan and hydrogen peroxide should be simultaneously fed to a portion of the hydrogen peroxide required for the reaction with exact analysis to effect flow control so as to be always an excess of H.sub.2 O.sub.2 in an excess amount in the extremely limited range more approximate to a stoichiometric amount to the raw material, an alkylmercaptan, and then the reaction steps become complicated, which leads to the drawback that both yield and purity of the so-obtained product may be variable.
Moreover, oxidation is carried out at a reaction temperature substantially beyond 60.degree. C. to afford many undesired by-products of impurities such as sulfuric acid or an organic acid. Furthermore, although a theoretically slightly excess amount of hydrogen peroxide is used to an alkylmercaptan, an amount of the hydrogen peroxide to be used is actually insufficient to complete oxidation of an alkylmercaptan under the aforementioned conditions, whereby, as a matter of fact, the reaction intermediates such as disulfides or the like may remain and the product may be contaminated.
Accordingly, the product prepared by this process is insufficient in a product purity to be applied for the general use of an alkanesulfonic acid, particularly, hydroxyethanesulfonic acid.
As explained above, the processes as described in U.S. Pat. Nos. 4,910,330 and 4,987,250 involves the serious problems as depicted above for the production using a scale-up or large equipment and thus they are not perfectly satisfactory in an industrial aspect.